A Wordnet from the Ground Up

3.3. Evaluation 59the number of LUs from the subtree of Q which are located at a close distance to Q.The problem is especially visible for question LUs in small hypernymy subtrees witha limited number of hyponyms. The problem appears in the case of any similaritymeasure based on the path length, so we have heuristically modified the measure byadding a constant δ R = 3 to any path going across the virtual root. Lower values ofδ R gave no visible changes, while the higher numbers caused a large reduction of thenumber of QA pairs.The difference in the level of difficulty between WBST+H and EWBST is illustratedin Figure 3.3 by an example problem generated by this method for the same QA pair:〈majątek (property, estate), mienie (property) 〉.EWBSTQ: majątek (property, estete)A: lokata (deposit, investment), mienie (property)obligacja (bond, stock), wkład (deposit, outlay)WBST+HQ: majątek (property, estete)A: dzieciuch (child, brat), mienie (property)rynsztok (gutter),stryj (uncle, father’s brother).Figure 3.3: Example of the difference between EWBST and WBST QA pairsSimilarly to the tests performed for WBST+H, we have assessed the influence ofthe evolution of plWordNet on the MSR performance in EWBST. The same algorithmof extraction was used as in the case of the former experiments: MSR GRW F (Lin)discussed in Section 3.4. Only a MSR for nominal LUs was built, because EWBSTdepend strongly on the hypernymy structure. The same MSR was tested with differentversions of EWBST produced from different archival versions of plWordNet. Theresults are presented in the joint Table 3.2. Examples of EWBST test instances arepresented in the Fig. 3.4.We can observe for EWBST results a similar tendency as for WBST+H. TheEWBST test becomes slightly easier as plWordNet evolves (we hope that it improves):from 64.81% to 69.75%. For EWBST, however, the increase is continuous with eachversion of plWordNet – WBST+H shows a larger difference only between the finalcore plWordNet and the expanded version. The increase for EWBST may be due tothe deepening of the hypernymy structure. There are two possible reasons for theobserved changes of the MSR results in relation to different tests. The introductionof many specific LUs in the expanded version of plWordNet made both tests easier:specific LUs are easier to distinguish. EWBST was getting easier with the deepeninghypernymic structure, as LUs grouped earlier in large vague synsets were distributed